Molecular architecture of human prion protein amyloid: A parallel, in-register β-structure

Abstract

Transmissible spongiform encephalopathies (TSEs) represent a group of fatal neurodegenerative diseases that are associated with conformational conversion of the normally monomeric and ␣-helical prion protein, PrP C , to the ␤-sheet-rich PrP Sc . This latter conformer is believed to constitute the main component of the infectious TSE agent. In contrast to high-resolution data for the PrP C monomer, structures of the pathogenic PrP Sc or synthetic PrP Sc -like aggregates remain elusive. Here we have used sitedirected spin labeling and EPR spectroscopy to probe the molecular architecture of the recombinant PrP amyloid, a misfolded form recently reported to induce transmissible disease in mice overexpressing an N-terminally truncated form of PrP C . Our data show that, in contrast to earlier, largely theoretical models, the conformational conversion of PrP C involves major refolding of the C-terminal ␣-helical region. The core of the amyloid maps to C-terminal residues from Ϸ160 -220, and these residues form single-molecule layers that stack on top of one another with parallel, in-register alignment of ␤-strands. This structural insight has important implications for understanding the molecular basis of prion propagation, as well as hereditary prion diseases, most of which are associated with point mutations in the region found to undergo a refolding to ␤-structure.EPR ͉ spin labeling ͉ transmissible spongiform encephalopathy

Conformational Properties of β-PrP

“…However, whereas the crystal structure of the ␣-helical domain-swapped dimer of PrP can be accommodated in ␤-PrP fibril subunits, the lack of significant ␣-helicity observed in the far-UV CD spectra of ␤-PrP oligomers and fibrils is inconsistent with this conformation constituting the fibril subunits (40). Furthermore, EPR measurements of recombinant PrP fibrils are consistent with a parallel, in-register ␤-sheet arrangement for the monomeric units dominating the conformations within the fibrils (77). Nevertheless, the disordered nature of the ␤-PrP precursor state parallels the behavior of the precursor states of a number of other amyloidogenic proteins (60, 78 -80), where the fluctuating, partially structured nature of these precursors appears to allow more readily the formation of specific intermolecular contacts required for the formation of higher order oligomers and fibrillar structures.…”

Dynamics of a truncated prion protein, PrP(113–231), from 15N NMR relaxation: Order parameters calculated and slow conformational fluctuations localized to a distinct region

“…It is yet to be established whether PrP Sc retains any of the structural elements found in PrP C , although recent data suggests that residues 160-220 undergo significant conformation change to form amyloid fibers. 13,24 In contrast, modeling based on 2D crystals, 46 and epitope mapping studies 47 of PrP C and PrP Sc , as well as the presence of the intra-molecular disulphide in PrP Sc , 48 suggests that much of helix B and C may be retained in the scrapie form. At face value, the J(0) values hint at the possibility that helix A of PrP C has relatively more flexibility than helix B and C. However, the effect of anisotropic tumbling needs to be taken into account.…”

“…[10][11][12] There has been some recent progress in defining the molecular architecture of prion amyloid fibers. 13,14 The mammalian prion proteins have a high homology at the sequence and structural level. All mammalian PrP C studied consist of two structurally distinct domains.…”

Overactivation of calcineurin induced by amyloid-beta and prion proteins

“…The PrP C is a cell membrane glycoprotein that can undergo disease-associated structural modifications, giving rise to a pathogenic isoform called scrapie prion protein (PrP Sc ) that accumulates as amyloid plaques in the brain of patients suffering from PRE (Barnham et al, 2006;Wisniewski and Sigurdsson, 2007). Recently, it was proposed that the Cterminal of a-helices in PrP C refolds into b-strands, which adopt a parallel alignment (Cobb et al, 2007). Both Ab and PrP Sc have a high b-sheet content, which renders them insoluble, resistant to proteolysis and neurotoxic (Soto, 1999;Wisniewski and Sigurdsson, 2007).…”